sign

A sign is any object, gesture, sound, or mark that conveys information or stands for something beyond itself. In semiotics, a sign comprises two parts: the signifier, the form that conveys the meaning, and the signified, the concept or referent to which it points. The relationship between signifier and signified is conventional and culturally dependent.

Signs appear in many forms: linguistic signs such as words and morphemes; visual signs such as drawings and symbols; and audio signs such as alarms or spoken cues. A sign can indicate an attribute (a warning label), a state (green light), or an instruction (do not enter).

In mathematics and logic, signs function to denote quantity, operation, or relation. The sign of a real number distinguishes positive and negative values; the sign function sgn(x) returns −1, 0, or 1. Other mathematical signs include plus, minus, equals, and integral signs, which carry standardized meanings.

Sign languages are fully developed visual-gestural languages used by deaf and hard-of-hearing communities worldwide, with grammar independent of spoken languages. They rely on hand shapes, movements, facial expressions, and body posture to convey meaning.

Road signs, public signs, and signage systems organize information for safety and navigation. They are governed by international and national standards to be recognizable and unambiguous.

As a verb, to sign means to write one’s name or to authorize a document. Signage is the collective term for signs displayed in public spaces, used for directions, warnings, branding, or information.